Encapsulation of Strongly Fluorescent Carbon Quantum Dots in Metal–Organic Frameworks for Enhancing Chemical Sensing

Silver Nanoclusters Encapsulated into Metal-Organic Frameworks with Enhanced Fluorescence and Specific Ion Accumulation toward the Microdot Array-Based Fluorimetric Analysis of Copper in Blood

Silver nanoclusters (AgNCs) were first coated with bovine serum albumin (BSA) and then encapsulated into porous metal-organic frameworks of ZIF-8 by the protein-mediated biomineralization process. Unexpectedly, the fluorescence intensities of the yielded AgNCs-BSA@ZIF-8 nanocomposites were discovered to be continuously enhanced during each of the BSA coating and ZIF-8 encapsulation steps. Compared to common AgNCs, greatly improved photostability and storage stability of AgNCs could also be expected. More importantly, having benefited from the ZIF-8 shells, the prepared nanocomposites could possess the specific accumulation and sensitive response to Cu²⁺ ions, resulting in the rational quenching of their fluorescence intensities. Moreover, AgNCs-BSA@ZIF-8 nanocomposites were coated onto the hydrophobic arraying slides toward a microdots array-based fluorimetric method for the fast and sensitive evaluation of Cu²⁺ ions. It was discovered that the developed fluorimetric strategy could ensure the high-throughput analysis of Cu²⁺ ions in wide pH range, and especially some harsh and high-salt media. It can allow for the detection of Cu²⁺ ions in blood with the concentrations ranging from 4.0 × 10^-4 to 160 μM, thus serving as a new copper detection candidate to be widely applied in clinical test, food safety, and environmental monitoring fields.

Mechanochromic MOF nanoplates: spatial molecular isolation of light-emitting guests in a sodalite framework structure

Mechanochromic materials have a wide range of promising technological applications, such as photonics-based sensors and smart optoelectronics. The examples of mechanochromic metal-organic framework (MOF) materials, however, are still relatively uncommon in the literature. Herein, we present a previously undescribed Guest@MOF system, comprising "Perylene@ZIF-8" nanoplates, which will undergo a reversible 442 nm ⇌ 502 nm photoemission switching when subjected to a moderate level of mechanically-induced pressure at several tens of MPa. The nanoplates were constructed via high-concentration reaction (HCR) strategy at ambient conditions to yield a crystalline ZIF-8 framework hosting the luminous Perylene guests. The latter confined within the porous sodalite cages of ZIF-8. Remarkably, we show that in a solid-state condition, it is the spatial isolation and nano-partitioning of the luminescent guests that bestow the unique solution-like optical properties measured in the host-guest assembly. As such, we demonstrate that switchable red- or blue-shifts of the visible emission can be accomplished by mechanically modifying the nanoscale packing of the nanoplates (e.g. monoliths, pellets). Theoretical calculations suggest that the elasticity of the host's sodalite cage coupled with the intermolecular weak interactions of the confined guest are responsible for the unique mechanochromic luminescence behavior observed.

A novel fluorescent sensor for water in organic solvents based on dynamic quenching of carbon quantum dots

A novel fluorescent sensor for water in organic solvents was proposed based on dynamic quenching of carbon quantum dots.

Carbon nanodots in ZIF-8: synthesis, tunable luminescence and temperature sensing

A new hybrid material CNDs@ZIF-8 with tunable luminescence and temperature-responsive photoluminescence has been synthesized by a low temperature-calcination method. An approximate white light has been achieved by combining the blue emission of ZIF-8 framework and the high yellow emission of CNDs.

Metal-Organic Framework-Based Sensors for Environmental Contaminant Sensing

Increasing demand for timely and accurate environmental pollution monitoring and control requires new sensing techniques with outstanding performance, i.e., high sensitivity, high selectivity, and reliability. Metal-organic frameworks (MOFs), also known as porous coordination polymers, are a fascinating class of highly ordered crystalline coordination polymers formed by the coordination of metal ions/clusters and organic bridging linkers/ligands. Owing to their unique structures and properties, i.e., high surface area, tailorable pore size, high density of active sites, and high catalytic activity, various MOF-based sensing platforms have been reported for environmental contaminant detection including anions, heavy metal ions, organic compounds, and gases. In this review, recent progress in MOF-based environmental sensors is introduced with a focus on optical, electrochemical, and field-effect transistor sensors. The sensors have shown unique and promising performance in water and gas contaminant sensing. Moreover, by incorporation with other functional materials, MOF-based composites can greatly improve the sensor performance. The current limitations and future directions of MOF-based sensors are also discussed.

Synthesis of graphene quantum dot/metal–organic framework nanocomposites as yellow phosphors for white light-emitting diodes

Graphene quantum dots (GQDs) and a metal–organic framework were assembled to form a nanocomposite for solving the GQDs’ fluorescence quenching problem in WLEDs.

Hydrothermal synthesis and crystal structure of a poly[aqua-(μ4-4-(carboxylatomethyl)benzoato-κ4O:O′:O′′:O′′′)-(μ2-1-(4-(1H-imidazol-1-yl)benzyl)-1H-1,2,4-triazole-κ2N:N′) dimanganese(II)], [Mn2(C9H6O4)2(C12H11N5)(H2O)]

C30H25N5O9Mn2, monoclinic, P21/c (no. 14), a = 15.5012(6) Å, b = 9.3423(3) Å, c = 19.7517(6) Å, β = 95.966(3)°, V = 2844.90(18) Å3, Z = 4, Rgt(F) = 0.0362, wRref(F2) = 0.0971, T = 293(2) K.

BSA-AuNPs@Tb-AMP metal-organic frameworks for ratiometric fluorescence detection of DPA and Hg2

An easy and effective strategy for synthesizing a ratiometric fluorescent nanosensor has been demonstrated in this work. Novel fluorescent BSA-AuNPs@Tb-AMP (BSA, bovine serum albumin; AMP, adenosine 5'-monophosphate; AuNPs, Au nanoparticles) metal-organic framework (MOF) nanostructures were synthesized by encapsulating BSA-AuNPs into Tb-AMP MOFs for the detection of 2,6-pyridinedicarboxylic acid (DPA) and Hg²⁺ . DPA could strongly co-ordinate with Tb³⁺ to replace water molecules from the Tb³⁺ center and accordingly enhanced the fluorescence of Tb-AMP MOFs. The fluorescence of BSA-AuNPs at 405 nm remained constant. While the fluorescence of BSA-AuNPs at 635 nm was quenched after Hg²⁺ was added, the fluorescence of Tb-AMP MOFs remained constant. Accordingly, a ratiometric fluorescence nanosensor was constructed for detection of DPA and Hg²⁺ . The ratiometric nanosensor exhibited good selectivity to DPA over other substances. The F₅₄₅ /F₄₀₅ linearly increased with increase of DPA concentration in the range of 50 nM to 10 μM with a detection limit as low as 17.4 nM. F₆₃₅ /F₄₀₅ increased linearly with increase of Hg²⁺ concentration ranging from 50 nM to 1 μM with a detection limit as low as 20.9 nM. Additionally, the nanosensor could be successfully applied for the determination of DPA and Hg²⁺ in running water.

Carbon dots: materials, synthesis, properties and approaches to long-wavelength and multicolor emission

Herein, we summarize recent research developments and progress of carbon dots (CDs), which have been attracting considerable attention as a new type of photoluminescent material. Raw materials, from single carbonaceous compounds to colorful natural substances, for the synthesis of CDs are discussed. A range of diverse synthetic methodologies to achieve better photoluminescence performance and more advanced functions are summarized, and these are basically divided into two classes: top-down and bottom-up. The inspiring properties, mainly including composites, optical properties and cytotoxicity, are listed. In particular, the luminescence mechanism and surface functionalization of the CDs are briefly discussed. Moreover, on the basis of the above, the long-wavelength and multicolor emission properties of CDs and ways to achieve these goals including surface state and size controlled by synthesis strategies, proper precursors, chemical doping and modification, solvatochromic effects and energy transfer are reviewed in detail.

Synthesis of Recombinant Mouse Crystallin Proteins and in Vitro Measurement of Their Refractivity

The eye lens is an organ that focuses light onto the retina and is reported to have a high refractive index in vertebrates. An analysis of refractivity was conducted using recombinant mouse Crystallin proteins produced in Escherichia coli (E. coli) compared with bovine serum albumin (BSA) and other commercially available proteins. Not only did we measure the refractivity but for one of the crystallins, Cryba1, we also confirmed that it responds uniquely to its environmental conditions. The crystallin showed high refractivity, as expected, and we confirmed that the electrical charge of the Cryba1 molecule influences its refractivity.

Zeolitic imidazolate framework 8 (ZIF-8) reinforced macroporous resin D101 for selective solid-phase extraction of 1-naphthol and 2-naphthol from phenol compounds

Macroporous resin has been attracting intensive attention due to its critical role in separation and purification of natural products. Herein, a zeolitic imidazolate framework 8 reinforced macroporous resin D101 was prepared via a room temperature growth method and used for dispersive SPE of 1-naphthol and 2-naphthol. The parameters affecting the adsorption and desorption efficiency such as the sample pH, adsorbent amount, extraction time, desorption solvent, and desorption time were investigated. The as-prepared adsorbent showed selectivity for 1-naphthol and 2-naphthol compared to other phenols. Under the optimum dispersive SPE conditions, the detection of 1-naphthol and 2-naphthol coupled with a CZE method was conducted and the LODs for 1-naphthol and 2-naphthol were 1.37 and 1.43 ng/mL, respectively. Moreover, the results of urine sample analysis showed the spiked recoveries to be in the range of 96.2-106.9%. This study indicated that D101@ZIF-8 (where ZIF is zeolitic imidazolate framework) is a promising selective adsorbent for the analysis of 1-naphthol and 2-naphthol in urine samples.

CoFe2O4@MIL-100(Fe) hybrid magnetic nanoparticles exhibit fast and selective adsorption of arsenic with high adsorption capacity

In this study, we report the synthesis and application of mesoporous CoFe₂O₄@MIL-100(Fe) hybrid magnetic nanoparticles (MNPs) for the simultaneous removal of inorganic arsenic (iAs). The hybrid adsorbent had a core-shell and mesoporous structure with an average diameter of 260 nm. The nanoscale size and mesoporous character impart a fast adsorption rate and high adsorption capacity for iAs. In total, 0.1 mg L⁻¹ As(V) and As(III) could be adsorbed within 2 min, and the maximum adsorption capacities were 114.8 mg g⁻¹ for As(V) and 143.6 mg g⁻¹ for As(III), higher than most previously reported adsorbents. The anti-interference capacity for iAs adsorption was improved by the electrostatic repulsion and size exclusion effects of the MIL-100(Fe) shell, which also decreased the zero-charge point of the hybrid absorbent for a broad pH adsorption range. The adsorption mechanisms of iAs on the MNPs are proposed. An Fe-O-As structure was formed on CoFe₂O₄@MIL-100(Fe) through hydroxyl substitution with the deprotonated iAs species. Monolayer adsorption of As(V) was observed, while hydrogen bonding led to the multi-layer adsorption of neutral As(III) for its high adsorption capacity. The high efficiency and the excellent pH- and interference-tolerance capacities of CoFe₂O₄@MIL-100(Fe) allowed effective iAs removal from natural water samples, as validated with batch magnetic separation mode and a portable filtration strategy.

Dual-emissive polystyrene@zeolitic imidazolate framework-8 composite for ratiometric detection of singlet oxygen

The co-encapsulation of EuPS and AnC in a ZIF-8 host leads to the formation of a dual-emissive composite for fluorescent ratiometric sensing of singlet oxygen.

Fluorescent carbon dots: rational synthesis, tunable optical properties and analytical applications

This review summarizes current advances on the design and the employment of fluorescent carbon dots in sensing applications, especially from the point of analytical view.

A novel metal–organic framework loaded with abundant N-(aminobutyl)-N-(ethylisoluminol) as a high-efficiency electrochemiluminescence indicator for sensitive detection of mucin1 on cancer cells

Abundant luminophore N-(aminobutyl)-N-(ethylisoluminol) functionalized metal–organic framework was synthesized as a novel and high-efficiency electrochemiluminescence indicator.

A dual-emission probe to detect moisture and water in organic solvents based on green-Tb3+ post-coordinated metal–organic frameworks with red carbon dots

A new dual-emission Tb³⁺@p-CDs/MOF (red carbon dots, green Tb³⁺) serves as a luminescent sensor for water and humidity, due to the agglomeration effect of p-CDs in different solvents.

Efficient photocatalytic and photovoltaic applications with nanocomposites between CdTe QDs and an NTU-9 MOF

CdTe QDs + NTU-9 MOF as a novel photoanode to improve the efficiency of a QD cell by about 1.5%.

Recent advances in nanomaterials for water protection and monitoring

Nanomaterials (NMs) for adsorption, catalysis, separation, and disinfection are scrutinized. NMs-based sensor technologies and environmental transformations of NMs are highlighted.

Visible detection of copper ions using a fluorescent probe based on red carbon dots and zirconium metal–organic frameworks

Specific spectral energy transfer leads to a gradually increasing quenching effect on the fluorescence of UiO-66-(COOH)₂with a higher concentration of Cu²⁺, causing a visible color change from blue to red.

An updated roadmap for the integration of metal–organic frameworks with electronic devices and chemical sensors

This review highlights the steps needed to bring the properties of MOFs from the chemical lab to the microelectronics fab.

Versatile design and synthesis of nano-barcodes

This review provides a critical discussion on the versatile designing and usage of nano-barcodes for various existing and emerging applications.

Lanthanide/nucleotide coordination polymers: an excellent host platform for encapsulating enzymes and fluorescent nanoparticles to enhance ratiometric sensing

The co-encapsulation of GOx and CDs endows the resulting composite with excellent catalytic and fluorescence activities and enhanced sensing performances.

MnO2in situ formed into the pores of C-dots/ZIF-8 hybrid nanocomposites as an effective quencher for fluorescence sensing ascorbic acid

Rapid construction of C-dots/ZIF-8 composites and in situ growth of MnO₂ into their pores as a quencher for ascorbic acid fluorescence sensing.

Insight into Understanding Dielectric Behavior of a Zn-MOF Using Variable-Temperature Crystal Structures, Electrical Conductance, and Solid-State 13C NMR Spectra

A Zn-based metal-organic framework (MOF)/porous coordination polymer (PCP), (EMIM)[Zn(SIP)] (1) (SIP^3- = 5-sulfoisophthalate, EMIM⁺ = 1-ethyl-3-methylimidazolium), was synthesized using the ionothermal reaction. The Zn²⁺ ion adopts distorted square pyramid coordination geometry with five oxygen atoms from three carboxylates and one sulfo group. One of two carboxylates in SIP^3- serves as a μ₂-bridge ligand to link two Zn²⁺ ions and form the dinuclear SBU, and such SBUs are connected by SIP^3- ligands to build the three-dimensional framework with rutile (rtl) topology. The cations from the ion-liquid fill the channels. This MOF/PCP shows two-step dielectric anomalies together with two-step dielectric relaxations; the variable-temperature single-crystal structure analyses disclosed the dielectric anomaly occurring at ca. 280 K is caused by an isostructural phase transition. Another dielectric anomaly is related to the dynamic disorder of the cations in the channels. Electric modulus, conductance, and variable-temperature solid-state ¹³C CP/MAS NMR spectra analyses revealed that two-step dielectric relaxations result from the dynamic motion of the cations as well as the direct-current conduction and electrode effect, respectively.

Modulating the optical properties of the AIE fluophor confined within UiO-66's nanochannels for chemical sensing

Transformation of aggregation induced emission (AIE) molecules into functional materials can greatly tune their fluorescence properties and expand their related potential applications. Here, we demonstrate a facile strategy to modulate the fluorescence properties of AIE molecules by confining them within the nanochannels of metal-organic frameworks (MOFs). AIE molecules (4,4'-(hydrazine-1,2-diylidene bis(methanylylidene)) bis(3-hydroxybenzoic acid), HDBB) with pH-dependent emission were successfully integrated into UiO-66 resulting in a UiO-66⊃HDBB complex while maintaining the crystal structure by the host-guest process. The fluorescence properties of HDBB can be modulated by virtue of the unique nanospace confining effect. Furthermore, UiO-66⊃HDBB was used as a sensitive and selective fluorescent probe for Cu²⁺ detection in aqueous solution. This study provides a facile strategy for the construction of high performance AIE based luminescent materials with adjustable properties for potential applications.

Carbon dots: surface engineering and applications

Carbon dots have attracted a great deal of attention because of their high performance, cheap and facile preparation, and potential applications in a wide area. In order to broaden their applications, especially to meet specific requirements, surface engineering, including tailoring surface functional group coating and subsequent chemical modification as required, is an effective strategy for further functionalization of carbon dots. In this article, representative approaches to coating the surface with various functional groups, and strategies for conjugating specific materials onto the surface of carbon dots for functional modification via covalent bonds, electrostatic interactions and hydrogen bonds are highlighted, as well as the results from explorations of their various applications in target modulated sensing, accurate drug delivery and bioimaging at high resolution.

Preparation of Silicon-Carbon-Based Dots@Dopamine and Its Application in Intracellular Ag(+) Detection and Cell Imaging

A novel nanocomposite, silicon-carbon-based dots@dopamine (Si-CDs@DA) was prepared using (3-aminopropyl) triethoxysilane, glycerol, and dopamine as raw materials via a rapid microwave-assisted irradiation. This type of Si-CDs@DA exhibited ultrabright fluorescence emission (quantum yield of 12.4%) and could response to Ag(+) selectively and sensitively. Moreover, the obtained Si-CDs@DA can be further applied in sensing intracellular Ag(+) and cell imaging, because of its photostability, salt stability, and low cytotoxicity. This study provides a simple and efficient approach for preparing novel Ag(+) fluorescent probes, which could expand the application of carbon nanomaterials in designing related biosensors.

One-step facile synthesis of novel β-amino alcohol functionalized carbon dots for the fabrication of a selective copper ion sensing interface based on the biuret reaction

The detection strategy of β-amino alcohol functionalized carbon dots for Cu²⁺ based on the biuret reaction.

In situ preparation of a MOF-derived magnetic carbonaceous catalyst for visible-light-driven hydrogen evolution

A MOF-derived magnetic carbonaceous photocatalyst was prepared in situ and demonstrated highly efficient visible-light-driven hydrogen evolution without noble metal cocatalyst.